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    O<sub>2</sub>  <br>

    x<sup>2</sup> <br>

    <b>粗体</b> <br>

    <!-- 语义更加强调 -->
    <strong>strong - java</strong> <br>

    <u>下划线</u>  <br>

    <i>斜体</i> <br>

    <!-- 语义更强调 -->
    <em>斜体</em> <br>

    3&ge;2  <br>
    2&lt;3 <br>
    &copy; <br>
    &reg;<br>
    空&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;格
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